A stress ribbon, or stressed ribbon, is one of the simplest forms for long span structures and is based upon the iron chain bridge developed in Asia over 2000 years ago. A typical stress ribbon bridge is constructed with the use of high strength steel cables or tendons, typically in the form of pre-stressing strands between two upright support structures. The deck for stress ribbon structures is typically reinforced concrete, but may be any structural system that is capable of resisting compression forces and has adequate axial stiffness. Initially, the deck system is suspended from the cable system in an unstressed state, though the weight of the deck serves to add tension to the cable system. Subsequently, the steel cables or tendons are tensioned to put the deck system in a compressive state, thereby creating a prestressed (precompressed) structural system, with significantly increased stiffness beyond the cable system alone. It is noted that, given the plurality of cables in each section, some portion of the cables may be used to support the weight of the deck and are termed “bearing cables” and the remaining portions used to precompress the deck and are therefore termed prestressing cables.
Incremental launching is a construction technique that has been developed for construction of bridges in circumstances where lifting activities are restricted or impossible, e.g., in circumstances where the structure is too high (such as a bridge spanning a deep valley or gorge) or where a busy highway or rail corridor is spanned and interruption of traffic represents a severe inconvenience. Through incremental launching, a portion, or segment, of the structure is constructed in a fixed location and pushed, or launched, over the feature to be spanned. During construction, the partially completed structure has to function as a cantilever resulting in increased load demands over those required in the final configuration, where the structure is supported at both ends. This typically requires a structure of increased depth and strength in order to meet the additional load demands during construction. Such structures must be, on average, 20% to 30% stronger and somewhat more costly as compared to conventional construction.